PPQS Flashcards
(205 cards)
1
Q
Suggest whteher clf3 HAS polar bonds
A
YES
- F more electronegative
- d+ cl, d- f
2
Q
electronegativity
A
ability of an atom to attract the bonding pair of ELECTRONSSS in a covalent bond
3
Q
why do repeats?
A
- increase repeatability
- find anomalies AND DISCARD
4
Q
atomic emission spectra provisde evidence for …
A
quantum shells
5
Q
6 MARKS
Problems and improvements of collection over water(gas collected 2 low)
A
- gas escapes from apparatus. use airtight bung with gas syringe
- metal covered with an oxide. clean with abrasive BEFORE weighing
- mass of metal used too low. use a more PRECISE balance
6
Q
shortest bond length in CH3OH
A
O-H as largest difference in electronegativity
7
Q
hydrogen bond angle
A
ALWAYS 180
- 2 bonding pairs
- 0 lone pairs
8
Q
trigonal bipyrmaidal angles
A
- 5 bp, 0 lp
- 90 and 120
9
Q
explain why the positive charge is on the carbon atom shown
A
tertairy carbocation is more stable than a primary carbocation
because it has more positive inductive alkyl groups
10
Q
importance of termination (2)
A
- 2 free radicals join together
- dont form any free radicals
11
Q
describe what is meant by cracking (2)
A
- use of high temperatures
- to break large molcules into smaller molecules, ,and produce alkenes
12
Q
why can propene form 2 possible products with HBr
A
- asymmetric alkene
- Br could join to c1 or c2
- to form 1 bromo or 2 bromo propane
13
Q
biggest hazard of alkanes
A
flamable
14
Q
in combustion where must the u-tube go
A
BEFORE boiling tube w lime water; distinguishes water as a product of combustion rather than the limewater
15
Q
why can hydrogen chloride gas not conduct electricity but HCl acid can
A
covalent bond in hydrogen chloride changes to an ionic bond in aqueous solution
16
Q
pressure in pvnrt is in
A
PASCALS
17
Q
EXPLAIN WHY METHANOL IS SOLUBLE IN WATER
A
- hydrogen bonding between them both
- of same strength
- comparable to the strength of the bonding in either component on its own
18
Q
why is NaCL soluble in water but not methanol
A
- hydration of BOTH ions in water
- but ionic bonding is stronger than bonding between ions and methanol
19
Q
2 reasons why x is more electronegative
A
- more protons
- smaller atomic radius
20
Q
despit ehaving polar bonds why is x not polar
A
- symmetricak
- BOND POLARITIES CANCEL
21
Q
use mexwell boltzmann diagram to explain why the use of a catalyst increases the rate of decomposition of ammonia (3)
A
- area under curve represents fraction of molecules with E>= Ea
- area with Ea of catalyst is greater; more molecules have E>= Ea
- more freqeunt successful collision
22
Q
similarities (2) and differences (2) between pi and sigma bonds
A
SIMILARITIES:
- both include the overlap of orbitals
- both involve electrostatic attraction between a BONDING pair of electrons and positive nuclei
DIFFERENCES:
- pi = sideways overlap of orbitals
- sigma = direct end on overlap of atomic orbitals
23
Q
explain maxwell boltzmann at high temp
A
- peak shifts to the right and lower
- at higher temperatures there are more particles with higher energy
24
Q
why might reaction not happen as shown
A
- might react with oxygen
- unlikely for reactants to be in correct ratio
- reaction must occur in a series of steps as too many particles reacting in equation
25
+- of chemical test vs infrared to show alcohol
+
cheaper
rapid
can be done in schools
-
CHEMICAL TEST NOT AS SENSITIVE
26
vol gas a bit higher at higher temp
gases expand when heated
27
why is the measurement of initial rate less accurate than max
- difficult to judge where tangent should be drawn for 0
- compared to other points on the line
28
why is a heterogeneous catalyst good for gas reactant
provides a surface for the reaction
29
why might uncertainty of someone else be hgiher with mass measurement
they used a smaller mass w same balance
30
why does catalyst not effect amount of product made
increases rate of forward and backward reactions
31
why is catalyst heated and why might it melt
- heated to provide activation energy
- metls as bonds broken
32
advatnage of catalyst iN INDUSTRY
- decreases activation energy
- allows milder conditions to be used (lowering cost)
33
chromate (VI) ion colour
YELLOW
34
TMS purpose
reference peak to compare other shifts to
35
what does NMR actually do
change spin state of hydrogen nuckeus
36
effect of increasing temp on rate constant
increases
37
why is there at least 2 steps (RDS REFERENCE)
- x and y in RDS (z not in)
- but more reactants in full equation
- so must be another step containing z
38
why is the major product from the tertiary carbocation
- most stable
- inductive effect of alkyl groups
39
why are the other reactant concnetrations in hUGE excess in iodine clock reaction
- concentration remain constant
- so that [I2] is limiting reagent; only its concnetration changes
-OTHERWISE A CURVE IS OBTAINED AS FULL ORDER OF REACTION
40
how to measure order of propanone as 1st order after already doing one step of iodine
- doulbe conc of propanone
- rate should double (gradient doubkes)
OR
- measure conc propanone over time
-constant half life
41
how to quench iodine TITRATION
- add NAHCO3
- neutralizes acid
42
sodium hydrogencarbonate neutralising ACID catalyst ionic equation
HCO3- + H+ = H2O + CO2
43
why is mols of soidum thiosulfate v low
- so concentration of reactants doesnt fall significantly before end point reached
- used up during initial rate period
44
quenching with IODINE CLOCK method
- take samples at various times
- quench with ice
- titrate using alkali
45
why might u get anomalies where rate is too high
- rate is too high
- reaction exothermic
- more collisions with E>= Ea
46
what happens if no thiosulfate added in iodine clock
reaction goes blue black immediately
47
purpose of thiosulfate
- as soon as iodide reacts to form iodine, thio reacts to turns it back to iodide
- to prevents colour change occuring until a set amuont of reaction occured
48
how to use colorimetry for iodoine(3)
- colorimetry
- measure absorbance
- CALIBRATION CURVE to turn it into concentration. absorbance proprotional to concentration
49
biggest alkane hazard
TOXIC BY INHALATION
50
reforming defition
converting straight chain HC to a ring/branched
51
cracking defintion
breaking a longer HC to shorter chain HC
52
describe waht happens to pi and sigma bonds in addition
- pi bond breaks
- sigma bond remains
- as pi weaker
- forms a carbocation intermediate
53
alkene with acidificed potassium manganate (7)
DILUTE SULFURIC ACID
- forms a DIOL
- purple to colourless
54
a fuel is ...
a substance that produces energy
55
why might the fuels be liquified
easier to transport
56
hazard vs risk
hazard: potential to do harm
risk: likelihood harm will result
57
which o the 2 ions has POLARIZING ability
cation
58
formation of acid rain rain on limestone
REACTS with limestone to corrode buildings
59
why conducgtivity different (ionic compounds)
cations are diff sizes
60
why cant silicon conduct electricity
- outer electorns FIXED in covalent bonds
- no delocalised electrons
61
why are polymers not sustainable
made from crude oil which is non-reneweable
62
why is pi weaker than sigma
- sigma direct end on overlap of orbitas- along line in between the 2 nuclei
- pi = sideways overlap
63
why is ice less dense than water
- molecules spread out further apart
- in ice water molecules in a LATTICE
- h bonds LONGER than covalent bonds
64
why non polar insoluble n water
cant h bond with water
65
ionic compounds solubility
- soluble in water, ions hydrated
- enthalpy change of hydration compensates for energy needed to break part lattice
- INSOLUBE in non polar as any forces that would form between ion and substance weaker than ionic bondng
66
describe the structure of. metal (3)
- lattice
- positive metal cations in layer
- sea of delocalised electrons
67
electrolyss of CuCrO4
- ions migrate
- Cu2+ blue colour towards cathode
- CrO4 2- yellow colour towards anode
68
2 sources of repulsion in ionic lattice
- ions of same charge repel
- positive nuclei repel
69
purpose of reforming
- more efficient combustion
- fuels with a higher octane number
- NO KNOCKING
70
why might volume co2 be slightly lower
- sligthyl soluble in water
71
using a smaller cylinder multiple times vs a bigger one once
1. look at error/ncertainty
2. more time taken to refill loads
3. GREATER TRANSFER LOSSES
72
why does distillation work
- difference in bp
- the one with lower bp boils and vaporises first, so can be condensed and then collected
73
purpose of reflux
- reactants vapourise, then condense
- return to reaction mixture
- allows to reach BP without LOSS OF REACTANT
74
HOW TO DISTILLATE TO GET PURE PRODUCT
1. heat
2. collect distillate
3. at BP of the prducrt
75
c-c with bromine vs c=c
1. c-c sigma only
2. strong bond, need to break c-h aswell
3. c=c sigma and pi
4. e- desnity above and below plane, polarises br-br
5. pi bond weaker so easier to break
76
2 conditions for cracking
1. high temp
2. silica catalyst
77
conditions for haloalkane and ammonia and why
- heat in a sealed vessel
- increases pressure to increase rate of reaction]
- but prevents loss of product
78
purpose of needing ethanol with the water and AgNO3 for haloalkane test
- cosolvent
- dissolves both haloalkane AND water
79
BP 2 chloro 2 methyl propane
50-52
80
rate of hydrolysis primary, secondary, tertiary
primary slowest
81
orbital
- a region where there is a high probaility of finding electrons
- holds up to 2 electrons with opposite spins
82
explain why 1st electron affinity is negative but second is positive
1. negative as exothermic due to attraction between POSTIIVE nucleus and electron
2. postivie as endothermic as energy required to overcome
3. repulsion between negative ion and electron
83
assumptions for theoretiacl lattice energy (2)
- 100% ionic bonding
- ions are perfect spheres
84
final comment for the theoretical lattice energy questions
- more energy released when making the bond, so bond is stronger, and LE more exothermic
85
2 problems with free radical substitution
1. cant control number of cl that will substiutte; oversubstitution
2. mixture of products will form, need to separate
86
) Explain why benzene is resistant to bromination but ethene reacts readily
with bromine at room temperature.
1. ethene c=c, electron density localised
2. electron density delocalised in pi structure of benzene
3. high ea for benzene as energy needed to break structure
4. ethene more susceptible to electrophilic attack
87
length hydrogen bonds compared to covalent
LONGER
88
BIGGEST DIFFERENCE BETWEEN ACID HYDROLYSIS OF ESTER AND ALKALI
acid: acid is catalyst
alkali: alkali is a REACTANT
89
why are condensation polymers biodegradable
ESTSER link can be hydrolysed by enzymes
90
temperature conditions for nitration of benzene and why
- below 55
- PREVENTS MULTIPLE SUBSTITUTIONS
91
Why is organic synthesis with less steps more eco frendly
higher yield
92
reaction to form no2 + for nitration of benzene
HNO3 + 2H2SO4 = 2HSO4- + NO2+ + H3O +
93
if Kp is x^2/y, discuss effect of incrasing pressure
- increases partial pressure of numerator more than denominator as squared
- so the mole fraction of y increases
- to resotre Kp
94
why hard to measure temp endo
difficult to measure temperature whilst heating
95
describe what happens when copper sulfate dissolves in water
- ionic lattice broken
- water hydrates each ion
96
why is HF boiling point the most
- F is MOST ELECTRONEGATIVE ELEMENT
- So stronger hydrogen bond
97
2 problems with NOx that arent ghg
- dissolve in water to form acid rain
- breathing problems
98
bond angle ice and water
different
99
eg Kc is 1
there are more moles of products than reactants explain
1. calculat new Kc; Kc >1
2. moles products must decrease AND moles reactants must increase to restore Kc
3. POE shifts to the left
100
test for halide
HNO3
AgNO3
101
WHAT SHAPE IS CATALYTIC CONVERTER AND WHY
- honeycomb
- increases SA
- allows gases to flow through
102
why cant distillation make ethanioc acid
- ethanol oxidised to ethanal
- low bp, distilled of as soon as formed
- before full oxidation to ethanoic acid
103
why would rate of reaction with oxygen decrease in a sealed vessel
concentration of oxygen decreases
104
ratio of 35 Cl 2 , 35Cl37Cl, 37Cl2
9:6:1
105
which apparatus for oxidation to ketone
- reflux
- to ensue full oxidation
106
why might a temperature reading be wrong
- mixture not stirred so temperature not unifor
107
who burns wiwth a sooty flame
greater c:h
eg alkenes
108
what does having a methyl group on the benzene ring do
INCREASE electron density
- positive inductive effect
109
if organic synthesis q, increase carbon chain how?
- if x1 : CN
- if loads: polymer
- if by a specific number of C : GRIGNARD
110
in complete oxidation the oxidising agent is
in excess
111
why might you get Cl 36 in mass spec
[35Cl37Cl]2+
m/z 36
112
steps of recrytallisation
- dissolve impure in MINIMUM volume of hot solvent
- filter it hot through a preheated funnel
- cool in ice bath + stir with glass rod
- vaccum filtration (buchner filtration)
- RINSE WITH ICE COLD ETHANOL
- dry between filter paper
113
distillation vs separating funnel
distillation: difference in BOILING POINTS
separating funnel: immiscible liquids
114
if one H+ is used in the reaction but 2 are produced, can it still be a catalyst?
YES
- One is regenerated, so thats the catalyst
- one is a product of the reaction
115
recrystallisation: why cool in ice bath
- product is less soluble in colder solutions so will crystallise out
116
recrystallisation: why warm filtering
- to prevent crystallisation
- which would reduce yeild
117
recrystallisation: why buchner filtration
- removes remaining solution (soluble impuirities) faster
- dryer crystals
118
problem if you have impurities in a gaseous reaction with a heterogeneous catalyst (3)
- impurities ADSORB onto surface of catalyst, occupying active sites
- fewer active sites avilable for reactants to adsorb
- IMPURITIES LESS LIKELY TO DESORB
119
purpose of TMS
- calibration
- to compare other hydrogen shifts
120
explain why you can get pcl5 but not ncl5
- PCl 5 can expand its octet
- NCl5 cannot as no d orbital
121
when halogenating with PCL5 , THE CONDITINO IS
anhydrous
122
how to classify something as an addition reaction
- 2 things react together
- only 1 product
123
colour of NO2
red brown gas
124
what acc happens when you add potassium manganate to an alkene
goes to a DIOL
125
3 suitable drying agents
CaCl2
MgSO4
Na2SO4
126
porblems with using a toxic fine powder
- risk of inhalation
- wear a face mask
127
consequence of condesner filled wrong
- air bubbles form
- less efficient cooling
- loss of reaction mixture
128
why do you need a condenser
PREVENT ESCAPE OF GAS
129
COMPARING SIMPLE DISTILLATION EQUIPMENT TO GOOD DISTILLATION EQUQIPMENT
SIMPLE:
- easy and chepaer to set up
- less efficient cooling
- gases will escape
BETTER:
- can check temp
- will condnse the vapour preventing escape
- therefore prederred AS can confirm when the product is being distilled and condenser ensures safe collection
130
how to ensure crystals reach the bottom of the tube
flick the tube
131
what is used as the liquid in the thiele tube and why ? (3)
1. dibutyl phthalate
2. HIGH BP
3. does not decompose at high temp
132
133
does oxygen react w sodium hydroxide
no
134
does co2 react with sodium hydroxide
yes
135
problem measuring temperature change of endo reation
difficult to measure temperature decrease whilst heating
136
problem with measuring temperature change of exothermic
- difficult to measure temperature of solid
-
137
Describe the processes that occur when solid copper(II) sulfate dissolves in water.
1. ionic lattice broken
2. ions hydrated
138
why does HF have higher mp than NH3
- similar LF
- both h bonds but
HF stronger as fluorine is MORE ELECTRONEGATIVE than N
139
why does x method give greater yeild
ONE STEP VS 2 STEP
- only forms one isomer
140
2 problems with the oxidese of nitrogen
- asthma
- dissolve in water to form acid rain
141
explain why pH increases so rapidly at the start of weak acid strong base titration (2)
- conc HA > conc A-
- ratio A- : HA changes in this region
-
142
hwen in doubt, assumption for acid base is:
conc acid initial = conc acid eqm
143
explain in terms of Kp what happens if u increase pressure
- increases num/denom more than the other
- Kp must be constant
- so mf of (prod or react) must increase/decrease
144
x ray diffraction in benzene
shows c-c all the same length
145
in sulfuric acid nitric acid describe their roles
sulfuric acid acts as acid , protonates the nitric acid which acts as a base
146
amine functional group
r-n-r
147
phenyl amine from nitrobenzene
- tin
- concentrated sulfuric acid
- SEPARATE WITH STEAM DISTILLATION
148
cu+ in nh3
[cu(nh3)2 ]+
colourless
149
MnO4 - and C2O4 2- reaction
- rate slow as they repel as negatively charged
- when Mn2+ formed, they catalyse the reaction
- Mn2+ REDUCES MnO4- to Mn3+
- and then mn3+ oxidises c2o4 2- to reform Mn2+
150
problem with metal oxides
- corrosive
react with silicone dioxide
forms INERT SILICATES
151
purpose of starch in iodine clock
- indicator
- turns blue black when all of thiosulfate ran out
- use TIME TAKEN for the blue black as an end point to calc initial rate
152
for the rate in halogenoalkane why use water and not oh-
oh- + ag would form ag(oh) ppt
153
WHY is eletrode potential mn2+ more positive than fe2+
- 3d5 half filled subshell more stable
- mn2+ has this so is more stable than mn3+
- fe3+ has this so is more stable than fe2+, also has pair of e- that repel so less stable
154
why are metals malleable but not ionic copounds?
- in a metal the layers of positive ions can slide over
one another (1)
* and sea of delocalised electrons between the
layers prevents repulsion between the ions in
one layer and those in another layer (1)
* in sodium chloride when a layer of ions is
displaced, ions with the same charge become close to one another and repel
155
burette uncertainty
0.05
156
2 dp balance uncertainty
0.005
157
why ight enthalpy of hydrogenation be less exo than expected (alkene)
- more stable
- DELOCALISATION OF double bonds (pi bonds)
158
in the C=- N dative covalent bond the lone pair is on the
C
159
for electrolysis, the colour of solution is
before its dischagred
eg cu2+ u just say blue
160
why issomething made in the body chiral (only oneenenationmer)
enzymes areusualy only specific to one enantiomer
161
kinetically stable means
- high ea barrier
- wont react without a catalyst or temp increase etc
162
thermodynamically unstable means
- gibbs >0
- products more stable than reactants ie the reaction happens
163
when an acid is diluted, degree of dissocaion
increases
164
c=c in a ring
no geometric isomerism
165
Explain why, when magnesium reacts with chlorine, MgCl2 is formed rather
than MgCl3.
- 3rd IE mg is very endothermic
- so the enthalpy of formation of mgcl3 is endothermic
- so not energetically favourable
166
explain esterification why delta h is close to but not exactly 0
- Same number and type of bonds are being broken
(in reactants) and made (in products)
- but the bonds are in different molecules/ environments
(so not exactly the same)
167
for a reaction where delta h is close to 0 explain effect of temp increase
- delta s surr = - delta h. / t
- as delta h v small, increase temp has little effect, so delta s total same
- AS DELTA S TOTAL = R LN K , k is also same
168
bonding in benzene
- 6 sigma bonds between carbons
- p orbitals overlap, to form delocalised electron pi system
169
why is that bond shown as a wedge
-chiral centre, shown as an optical isomer
- shows the tetrahedral, wedge means bond is in front of the plane of the paper
170
what happens if u forget to acidify the mno4- ?
- forms MnO2 (brown ppt)
- lower titre as
- only oxidises with 3 electrons vs 5
171
method to see how much free cl- in 3 diff solutions
- equal volumes of each soln
- add AgNO3 until in xs (no more ppt forms)
- filter, dry
- measure mass AgCl
- find moles
172
assess the feasibiltiy of x reation in alkali conditions e cell -0.03
- e cell v close to 0, not v negative
- increase the conc of alkali, shift poe to the right
173
if you give answer eg 1.2345 but your percentage unceratinty is 1.38% whats the prob
- give uncertainty to 2/3 sf
- as percentage uncertainty is greater than 0.2345
174
how can fe2+ form fe3+ in AQEUOUS SOLUTION
- ref 3rd ionisation energy is very endothermic
- but recovered by enthalpy of hydration of fe3+ is extremely exothermic
- more exo than that of fe2+ due to higher charge, smaller IR
175
how does the fe2+ lower activation energy
- in the og reaction involves 2 negatively charged ions reaction
- repulsion
- vs catalysed means positive and negative react: lower ea more kinetically favourable
176
what is the assumption in using 1/t for rate
-the methyl red is decolourised early in the reaction during initial rate period
-when the concentration of reactant vs time graph is
(almost) linear
-so the gradient of the tangent to the graph is the same as the (change in) concentration / time
177
Another student accidentally measured 8.5cm3
of potassium bromate(V)
rather than 8.0cm3 in Run 4.
Explain whether or not this portion of potassium bromate(V) should be discarded
- NO, as long as total volume remains the same
- as data is plotted on a graph, so not really important, just plot for the accurate volume
178
why not use a burette to transfer liquid for clock reaction
the burette would transfer the liquid too slowly (so the
start time would be inaccurate)
179
State the changes that you would make to the procedure to obtain the data
needed to determine the overall rate equation for the reaction between bromide
and bromate(V) ions in acid conditions.
- repeat for both
- making sure volume of bro3- is always constant
- total volume constant
- and vary just the volumes of bromide and h+
180
advantage of buchner (2)
- faster
- and drier product
181
why is f so DIFFICULT TO POLARISE
- small ionic radius
- single charge
- ELECTRON CLOUD HARDER TO DISTORT
182
SUGGEST why a gas container is so heavy
- thick walls
- to withstand high pressure
183
problems w polymers
- not biodegrabale, build up in landfill
- incineration RELEASES TOXIC GASES
- not all can be recycled
184
why is ammonia reaction in a sealed vessel
to prevent loss of ammonia gas
185
why is the extrapolation method greater
- heating not instantaneous
- so line of best fit accounts for if theres cooling during the reaction
186
improve the extrapolation method
- use a pipette incstead of measuring cylinder => lower percentage uncertainty
- measure temp at smaller interavls => MORE ACCURATE EXTRAPOLATION
- LID = prevent heat loss
187
first step of testing a SOLID for chloride ions
DISSOLVE IN WATER
then add hno3
agno3
white ppt
188
consideration when using PCl5
REACTS W WATER aswell !!!!
189
why is that the suggested range to boil off x compound
- the range starts below the boiling temperature of x and finishes below that of the others
- minimises the amount of the other compounds that could distil asw
190
alternative reason to prevent bumping
so the reaction mixture doesnt go into the condenser
191
why cool slowly and add slowly
- reaction is v vigorous and exothermic
- prevents evaporation of x as it has a low boiling point
192
advantage of alkali fuel cell vs acid
the catalyst is more efficient
193
Explain why the N-phenylanthranilic acid is added to the sodium hydroxide
solution before it is mixed with water in the preparation of this solution
-reacts w the sodium hhydroxide to form sodium carboxylate salt
- more soluble in water as ionic
194
ammonia specific test
- glass rod w hcl, hold in the gas
- dense white smoke
195
why add naoh drop by drop to transition metals
ppt may dissolve, so mask colour change
196
why rinse salt with etahnol (1)
and why is it cold (1)
- salt less soluble in ethanol than water
- and solubility decreases with temp decrease
197
relative ISOTOPIC mass
mass of an atom of an isotope relative to 1/12 carbon 12 atom
198
relative ATOMIC mass
weighted mean mass of an atom of an element relative ot 1/12 c-12 atom
199
cl isotope ratios
cl 35:cl 37
3:1
200
first ionisation energy
energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions
201
successive ionisation energies
energy required to remove each successive electron from a gaseous ion of an element under standard conditions
202
why do successsive IE increase
- electron taken from increasingly positive ion
- same number of protons attrating fewer e-
- stronger esa, smaller IR, more E required
203
orbital is
l is a region within an atom that can hold up to two electrons
with opposite spins
204
evidence of ions electrolysis
NOT DISCHARGED
eg Cu2+ CrO4 2-
cu2+ goes to the cathode and blue
CrO4 2- goes to the anode and yellow
green ish colour in the middle
must be molten or in solution for it to conduct Electricity
205
competitive exclusion
- 2 populations occupy the same niche
- interspecific competition for food, space etc
- the least adapted one is out competed
- ges extinct
